mod_auth_openidc is an authentication/authorization module f… (CVE-2021-39191)

Summary

Vulnerability reported (CVE-2021-39191). Risk of unauthorized operations or information disclosure. Exploitable via target_link_uri.

Original description

The description as published by the source.

mod_auth_openidc is an authentication/authorization module for the Apache 2.x HTTP server that functions as an OpenID Connect Relying Party, authenticating users against an OpenID Connect Provider. In versions prior to 2.4.9.4, the 3rd-party init SSO functionality of mod_auth_openidc was reported to be vulnerable to an open redirect attack by supplying a crafted URL in the target_link_uri parameter. A patch in version 2.4.9.4 made it so that the OIDCRedirectURLsAllowed setting must be applied to the target_link_uri parameter. There are no known workarounds aside from upgrading to a patched version.

Source: OSV.dev (Open Source Vulnerabilities) NVD GitHub Advisory OSV

Auto-generated summary

Assembled by SecPulse from the source data (CVSS, CWE, affected versions) using templates — no AI involved. Check the original description and references below for exact details.

A vulnerability tracked as CVE-2021-39191 has been found.
Attackers can target a specific entry point like target_link_uri over the network to misuse the product.
Risk of unauthorized operations or information disclosure.
What to do: apply the vendor's official patched release.
If unsure, ask your IT team or search "CVE-2021-39191" on the vendor's site.

CVE-2021-39191
Attack vector: remote (network-reachable) / unauthenticated
Attack surface: target_link_uri / OIDCRedirectURLsAllowed
Plan: 1) Audit SBOM/dependencies, 2) Stage→prod upgrade, 3) Add WAF/proxy monitoring on affected endpoints, 4) Hunt IOCs in logs.
Refs: see the GHSA / vendor advisory / patched release linked on this page.

❓ What is the problem

A vulnerability (unclassified) has been reported. Attackers reach the vulnerable code path via target_link_uri without authentication.

📍 Affected scope

Check the vendor advisory for the affected versions. Attack surface: target_link_uri / OIDCRedirectURLsAllowed.

🔥 Severity

Severity: ?. Risk of unauthorized operations or information disclosure.

🔧 How to fix

Update to the patched release per vendor advisory.

🛡️ Workaround

Until the patch is applied: disable the affected feature, apply WAF rules, or restrict access via network ACLs.

🔍 Detection

Search webserver/proxy logs for unusual request patterns matching this CVE's known IOCs. Audit SBOM/dependencies to find affected services.

Response actions

Concrete steps and command examples for SOC/SRE teams to execute in order

1
Identify exposure identify
```
Audit SBOM/dependencies for affected components.
```
資産台帳・SBOM・依存マニフェストで影響コンポーネントを特定する。
2
Post-deployment verification verify
```
Confirm patched version is live in production
```
パッチ適用後、ステージングで PoC または同等の悪用パターンを再現して脆弱性が閉じたことを確認。本番ではアクセスログ・WAF でアラート再発が無いか継続監視。

Fix status by distribution

Fixed packages published by each distribution for this CVE

Debian DEBIAN-CVE-2021-39191 libapache2-mod-auth-openidc Fixed in: 2.4.9.4-1

mod_auth_openidc is an authentication/authorization module for the Apache 2.x HTTP server that functions as an OpenID…